At the present time, there are a large number of different types of hydraulic or other lifts available. Generally, these are designed within the constraints set by the design requirements of the lift, such as lifting capacity, lifting heights, and costs of materials and individual components. As such, conventional designs represent a compromise between these different requirements.
The assignee of the present invention has previously developed an hydraulic lift for motor vehicle, which includes two separate scissor mechanisms, each for one side of the lift (U.S. Pat. No. 4,724,930). Each scissor mechanism lifts a corresponding elongate wheel deck, intended to support the wheels on one side of the vehicle. Beneath each scissor mechanism, there is a base unit, on which rollers of the scissor mechanism run. This leaves a significant space between the two wheel decks, which is largely unobstructed. Each scissor mechanism and its associated wheel deck has a respective hydraulic cylinder for raising and lowering it. To ensure that the two wheel decks are maintained at the same height, there is a cross brace between them, and also the hydraulic circuit includes a valve arrangement, to ensure that the flows to and from the two hydraulic cylinders are essentially the same. Such a lift can be dimensioned to lift a vehicle to a considerable height.
Such a hydraulic lift has a number of advantages. However, it is relatively large, heavy and immobile.
In particular, the provision of the base units renders the lift suitable only for a fixed installation. The bases support and guide the scissor mechanisms. They also ensure that the load is distributed to the underlying floor, so that the floor need not be particularly flat or smooth.
Similarly, there are available a variety of lifts intended to lift a vehicle off its wheels, causing the vehicle to be supported directly at its body or chassis. To raise the deck, there are a number of vertical posts, fixed to the ground around the deck, for example, 2 or 4 posts. The assignee of the present invention has developed such a 2 post lift (U.S. Pat. No. 4,976,336). Then, some sort of a mechanism is provided within or associated with the posts, for raising the deck.
Like the foregoing lift based on a scissor mechanism, this suffers from the advantage that it is essentially large, cumbersome and fixed installation.
There are also available so-called low rise lifts. As compared to a full rise lift which can achieve a lift of 6 feet, a low rise lift may provide a lift in the range of the order of 23-28 inches. The intention is to raise a vehicle sufficiently high to facilitate work that really only requires exterior access, e.g. brake work requiring access to the wheel hubs. Low rise lifts would not be used for work requiring access to the underside of the vehicle.
However, low rise lifts known to the assignee of the present invention, suffer from a number of disadvantages. Firstly, the lifting range of such low rise lifts is usually inadequate. Thus, even at full height, they will leave the wheel hubs and the like of a vehicle at a height that is too low to be truly comfortable for a mechanic to work on the brakes, suspension, etc.
Secondly, to the assignee's knowledge, most such low rise lifts rely on a parallelogram mechanism. As such, the wheel deck is pivotally connected to the ends of two arms, forming two parallel sides of the parallelogram. The other, lower ends of the arms, are pivotally secured to the ground.
It will be appreciated that, in initial lifting, the two arms are essentially close to the horizontal. As such, the wheel decks are cantilevered away, either in front of or behind, the ground pivot supports for the arms. For this reason, it is essential that the arms be securely attached to the ground.